Hydraulic Conductivity, Immobile Water Content, and Exchange Coefficient in Three Soil Profiles

2006 ◽  
Vol 70 (4) ◽  
pp. 1272-1280 ◽  
Author(s):  
L. Alletto ◽  
Y. Coquet ◽  
P. Vachier ◽  
C. Labat
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Profiles ◽  
Exchange Coefficient ◽  
Immobile Water

Field measured mobile water fraction for soils of contrasting texture

Soil Research ◽  
2000 ◽  
Vol 38 (6) ◽  
pp. 1131 ◽  
Author(s):  
A. E. A. Okom ◽  
R. E. White ◽  
L. K. Heng
Keyword(s):  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Water Content ◽  
Time Scale ◽  
Solute Transfer ◽  
Water Fraction ◽  
Mobile Water ◽  
Immobile Water ◽  
Mobile Fraction ◽  
Fertiliser Application

For the purpose of modeling solute transport, soil water has often been simply divided into an essentially mobile fraction, q m , which is active in solute transport, and an apparently immobile fraction, q im . Distinction between q m and q im was sought using the disc permeameter technique. This study examines unsaturated estimates of mobile water content at suction heads, h, of 20, 40, 80, and 120 mm for several soils ranging in texture from sand to clay. Following infiltration of 35 mm depth of 0.01 M KBr into initially dry soils, soil samples were collected from below the base of the disc permeameter and analysed for tracer concentrations which enabled partitioning of mobile and immobile water. Hydraulic conductivity and sorptivity were also derived from the infiltration data. The results show the expected non-linearity of hydraulic conductivity and sorptivity with suction. The mobile water expressed as a fraction, f, of the volumetric water content q (f = q m / q ) was generally found to range from 0.7 to 0.95, with an average of 0.85. The exception was one site for which f was ª 0.50. These values of f are comparable to those derived from leaching studies reported in the literature. An important finding of this work is that within the range of suctions measured, the mobile fraction was independent of suction. A possible explanation for this observation is that the soil capillary forces were dominant during the time scale of the experiment and therefore rapidly drew the invading solution. This finding could have important implications for fertiliser application. Furthermore, this result suggests that the assumption of a negligible solute transfer coefficient, a , between the mobile and immobile domains may be valid within the time scale of this method of measuring the mobile water content.

Parameterisation of physically based solute transport models in sandy soils

Soil Research ◽  
2003 ◽  
Vol 41 (4) ◽  
pp. 771 ◽  
Author(s):  
Y. M. Oliver ◽  
K. R. J. Smettem
Keyword(s):  
Solute Transport ◽  
Water Content ◽  
Mass Exchange ◽  
Granular Media ◽  
Sandy Soils ◽  
Exchange Coefficient ◽  
Water Fraction ◽  
Immobile Water ◽  
Mass Exchange Coefficient ◽  
Tracer Experiments

Immobile water fractions of up to 40% had been reported in sands, and it was therefore relevant to determine if the convection-dispersion equation (CDE) or mobile-immobile model (MIM) should be used as the basic physical model for field studies of solute transport in sandy soils. A review of literature data for granular media indicated that for steady state flow, the dispersion coefficient could be estimated from the grain Peclét number and the mass exchange coefficient from the pore water velocity, but the immobile water fraction was poorly predicted from soil properties.In this study, performed on a sandy soil at Moora, Western Australia, the choice of model was determined after analysis of column effluent breakthrough curves (BTC), sequential tracer experiments, and single tracer experiments on the same core. The latter two methods have recently been introduced in an attempt to independently measure some of the MIM parameters (immobile water content and mass transfer exchange coefficient) in situ. Low immobile water content was found in this sand, with very rapid exchange between the mobile and immobile regions. All 3 techniques gave measured immobile water contents around 10%, which was consistent with most literature values for granular media. The single tracer experiment does not give the mass exchange coefficient α (h–1), but α determined by the sequential tracer technique could not be confirmed by the BTC technique due to the wide 95% confidence interval of the fitted parameter. Although the MIM behaviour was minor and inconsistent in the Moora sand, the choice of model may depend on the problem under consideration. For short column experiments, the CDE and MIM produced similar solute transport behaviour. However, for leaching below the root-zone, the MIM is recommended.

scholarly journals Immobile Water Content and Mass Exchange Coefficient of a Field Soil

1997 ◽  
Vol 61 (4) ◽  
pp. 1030-1036 ◽  
Author(s):  
F. X. M. Casey ◽  
R. Horton ◽  
S. D. Logsdon ◽  
D. B. Jaynes
Keyword(s):  
Water Content ◽  
Mass Exchange ◽  
Field Soil ◽  
Exchange Coefficient ◽  
Immobile Water ◽  
Mass Exchange Coefficient

Hyphal colonization of Rhizophagus irregularis increases unsaturated hydraulic conductivity of a loamy sand distant from roots

2021 ◽  
Author(s):  
Michael Bitterlich ◽  
Richard Pauwels
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Hydraulic Properties ◽  
Volumetric Water Content ◽  
Rhizophagus Irregularis ◽  
Loamy Sand ◽  
Soil Hydraulic Properties ◽  
Unsaturated Hydraulic Conductivity ◽  
Soil Hydraulic ◽  
Root Exclusion

<p>Hydraulic properties of mycorrhizal soils have rarely been reported and difficulties in directly assigning potential effects to hyphae of arbuscular mycorrhizal fungi (AMF) arise from other consequences of AMF being present, i.e. their influence on growth and water consumption rates of their host plants that both also influence soil hydraulic properties.</p><p>We assumed that the typical nylon meshes used for root-exclusion experiments in mycorrhizal research can provide a dynamic hydraulic barrier. It is expected that the uniform pore size of the rigid meshes causes a sudden hydraulic decoupling of the enmeshed inner volume from the surrounding soil as soon as the mesh pores become air-filled. Growing plants below the soil moisture threshold for hydraulic decoupling would minimize plant-size effects on root-exclusion compartments and allow for a more direct assignment of hyphal presence to modulations in soil hydraulic properties.</p><p>We carried out water retention and hydraulic conductivity measurements with two tensiometers introduced in two different heights in a cylindrical compartment (250 cm³) containing a loamy sand, either with or without the introduction of a 20 µm nylon mesh equidistantly between the tensiometers. Introduction of a mesh reduced hydraulic conductivity across the soil volumes by two orders of magnitude from 471 to 6 µm d<sup>-1</sup> at 20% volumetric water content.</p><p>We grew maize plants inoculated or not with Rhizophagus irregularis in the same soil in pots that contained root-exclusion compartments while maintaining 20% volumetric water content. When hyphae were present in the compartments, water potential and unsaturated hydraulic conductivity increased for a given water content compared to compartments free of hyphae. These differences increased with progressive soil drying.</p><p>We conclude that water extractability from soils distant to roots can be facilitated under dry conditions when AMF hyphae are present.</p><p> </p>

Effects of textural layering on water regimes in sandy soils in a desert-oasis ecotone, Northwestern China

2021 ◽  
Author(s):  
Chengpeng Sun ◽  
Wenzhi Zhao ◽  
Hu Liu ◽  
Yongyong Zhang ◽  
Hong Zhou
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Water Infiltration ◽  
Northwestern China ◽  
Soil Profiles ◽  
Burial Depth ◽  
Layered Soils ◽  
Water Regimes ◽  
Desert Oasis

<p>Textural layering of soil plays an important role in distributing and regulating resources for plants in many semiarid and arid landscapes. However, the spatial patterns of textural layering and the potential effects on soil hydrology and water regimes are poorly understood, especially in arid sandy soil environments like the desert-oasis ecotones in northwestern China. This work aims to determine the distribution of textural layered soils, analyze the effects of different soil-textural configurations on water regimes, and evaluate which factors affect soil water infiltration and retention characteristics in such a desert-oasis ecotone. We measured soil water content and mineral composition in 87 soil profiles distributed along 3 transects in the study area. Constant-head infiltration experiments were conducted at 9 of the soil profiles with different texture configurations. The results showed that textural layered soils were patchily but extensively distributed throughout the study area (with a combined surface area percentage of about 84%). Soil water content in the profiles ranged from 0.002 to 0.27 g/cm<sup>3</sup> during the investigation period, and significantly and positively correlated with the thickness of a medium-textured (silt or silt loam) layer (<em>P</em> < 0.001). The occurrence of a medium-textured layer increased field capacity (FC) and wilting point (WP), and decreased available water-holding capacity in soil profiles. Burial depth of the medium-textured layer had no clear effects on water retention properties, but the layer thickness tended to. In textural layered soils, smaller water infiltration rate and cumulative infiltration, and shallower depths of wetting fronts were detected, compared with homogeneous sand profiles. The thickness and burial depth of medium-textured layers had obvious effects on infiltration, but the magnitude of the effects depended on soil texture configuration. The revealed patterns of soil textural layering and the potential effects on water regimes may provide new insight into the sustainable management of rainfed vegetation in the desert-oasis ecotones of arid northwestern China and other regions with similar environments around the world.</p>

scholarly journals Hydraulic Conductivity of Polymer-Amended Sand-Bentonite Backfills Permeated with Lead Nitrate Solutions

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Sheng-Qiang Shen ◽  
Ming-Li Wei
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Applied Pressure ◽  
Lead Nitrate ◽  
Bound Water ◽  
Liquid Limit ◽  
Filter Press ◽  
Diffuse Double Layer ◽  
Comparison Results ◽  
Pb Concentration

Hydraulic conductivity of sand-bentonite (SB) backfills amended with polyanionic cellulose (PAC) to lead nitrate (Pb(NO3)2) solutions was evaluated experimentally in this study. PAC-amended sand-bentonite (PSB) backfills were synthesized by mixing sand-bentonite mixture with 0.3 to 1.2% dry PAC (by total dry mixture mass) and mixed with a certain weight of conventional bentonite (CB) slurry. The rheology properties including the filtrate loss, viscosity, density, and pH testes of slurry with various bentonite dosages were measured to determine the reasonable CB dosage of slurry. The slump tests on PSB backfills with various mass slurries were conducted to determine the corresponding water content of backfills with slump 125 ± 5 mm. Under the applied pressure 100 kPa, the hydraulic conductivity to Pb(NO3)2 solutions (kc) of PSB backfills with various PAC contents was evaluated based on the modified filter press (MFP) tests, to ascertain the optimum PAC content of PSB backfills when permeated with Pb(NO3)2 solutions. Index properties, including the specific gravity (Gs) and liquid limit (wL) of PSB backfills, were measured after MFP tests. The MFP tests for PSB backfills were then conducted under various applied pressures to obtain the relationship between void ratio (e) and hydraulic conductivity of backfills. Finally, the flexible-wall permeability test (FWP test) under osmotic pressure 100 kPa was conducted to verify the effectiveness of the MFP test. The results indicate that slurry with 8% bentonite dosage is the reasonable choice in slurry wall construction. PSB has lower GS and higher wL compared to SB; increasing Pb concentration leads to GS of PSB increased and wL of PSB decreased. PSB with 0.6% PAC content is supposed as the optimum proportion of backfills when permeated with concentrated Pb(NO3)2 solution. PAC adsorbs large amount of bound water, which leads to higher water content (w) and e of PSB backfills, while lead ions (Pb) cause the diffuse double layer (DDL) of bentonite compressed and e of PSB backfills reduced. The kc of PSB-0.6 remains lower than 10−9 m/s and increases less than 10 times though the Pb concentration was up to 500 mM, demonstrating that the hydraulic performance of backfills can be improved effectively in Pb(NO3)2 solution by the additive PAC. The comparison results between k from MFP tests and FWP tests show that the MFP test is an effective and easy evaluation of hydraulic conductivity of backfills.

Hydraulic Conductivity of Compacted Tropical Clay Treated with Rice Husk Ash

2011 ◽  
Vol 367 ◽  
pp. 63-71 ◽  
Author(s):  
Adrian O. Eberemu ◽  
Agapitus A. Amadi ◽  
Joseph E. Edeh
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Rice Husk ◽  
Industrial Waste ◽  
Rice Husk Ash ◽  
Waste Product ◽  
Dry Density ◽  
Waste Containment ◽  
Hydraulic Behaviour ◽  
Waste Containment Systems

Laboratory study on compacted tropical clay treated with up to 16% rice husk ash (RHA), an agro-industrial waste; to evaluate its hydraulic properties and hence its suitability in waste containment systems was carried out. Soil-RHA mixtures were compacted using standard Proctor, West African Standard and modified Proctor efforts at-2, 0, 2 and 4% of optimum moisture content (OMC). Compacted samples were permeated and the hydraulic behaviour of the material was examined considering the effects of moulding water content, water content relative to optimum, dry density and RHA contents. Results showed decreasing hydraulic conductivity with increasing moulding water content and compactive efforts; it also varied greatly between the dry and wet side of optimum decreasing towards the wet side. Hydraulic conductivity generally decreased with increased dry density for all effort. Hydraulic conductivity increased with rice husk ash treatment at the OMC; but were within recommended values of 1 x 10-7 cm/s for up to 8% rice husk ash treatment irrespective of the compactive effort used. This shows the suitability of the material as a hydraulic barrier in waste containment systems for up to 8% rice husk ash treatment and beneficial reuse of this agro-industrial waste product.

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